A378915 Positive integers k such that k is not divisible by sigma(m) for any m >= 2, where sigma is the sum-of-divisors function (A000203).

1, 2, 5, 10, 11, 17, 19, 22, 23, 25, 29, 34, 37, 41, 43, 46, 47, 50, 53, 55, 58, 59, 61, 67, 71, 73, 79, 82, 83, 85, 86, 89, 94, 95, 97, 101, 103, 106, 107, 109, 113, 115, 118, 122, 125, 131, 134, 137, 139, 142, 145, 146, 149, 151, 157, 163, 166, 167, 170, 173

Offset: 1

Author

Paolo Xausa, Dec 11 2024

Keywords

• nonn

Links

• Paolo Xausa, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to sigma(n)

Crossrefs

Positions of ones in A378913.

Cf. A000203.

Programs

Mathematica

With[{upto = 500}, Table[If[Count[Divisible[n, #[[;; n]]], True] == 1, n, Nothing], {n, upto}] & [DivisorSigma[1, Range[upto]]]]

PARI

isok(m) = for(k=2, m, if (!(m % sigma(k)), return(0))); 1; \\ Michel Marcus, Dec 12 2024